DHCP duplicate leases

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This topic contains 9 replies, has 8 voices, and was last updated by Avatar Andrew Molan 5 years ago.

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    markdavies
    Member
    #164395

    Hello,

    I have a Windows Server 2008 domain controller with DHCP installed, this server is called “exchange”. I moved the DHCP services off a Windows Server 2003 a few weeks ago. It gives out DHCP to PC’s and everything without an issue. One thing it does though for some strange reason is in the list of leases it keeps getting lots of entries for my “terminalserver” and the “exchange” server, both of which are set with static IP addresses! I dont have any reservations set for these servers but I have excluded their static IP’s using the exclusions.
    Both of these servers are Virtual Machines running on VMWare platform, the main server called “exchange” has an E1000 virtual network card and the “terminalserver” has a VMXNET 3 virtual network card.

    I’ve checked for any duplicate DNS entries for these servers and there are no issues from what I can see.

    The problem it’s causing is that there aren’t many available IP’s anyway so when these servers take about 8 each its robbing the only remaining addresses.
    To temporarily get around the problem I go into the list of DHCP leases and just delete all the entries for these two servers.

    Any ideas of a solution to permanently stop this happening?
    Thanks a lot
    Mark

    Blood
    Blood
    Moderator
    #336598

    Re: DHCP duplicate leases

    Do the servers host remote access solutions, or have they done so in the past? I see this when remote access servers grab a handful of addresses for VPN clients.

    Avatar
    teendicked
    Member
    #388358

    Re: DHCP duplicate leases

    Hi thanks for your reply! The terminal server does have Routing and Remote access setup on it yes. However the server grabs way more IPs from DHCP than the amount of VPN connections that are being used. Also the exchange server never has had any remote access setup on it and it’s a brand new virtual machine…

    Blood
    Blood
    Moderator
    #336599

    Re: DHCP duplicate leases

    The routing and remote access role will generally grab between 8 and 10 regardless of how few connections are made. We only have 4 people using the VPN at any one time, but the server always has about 10 addresses available.

    I don’t know how the Exchange server might function in this regard.

    What other roles/features/applications are installed? Perhaps one of those is grabbing the addresses.

    tehcamel
    tehcamel
    Moderator
    #359866

    Re: DHCP duplicate leases

    markdavies;287086 wrote:
    Hi thanks for your reply! The terminal server does have Routing and Remote access setup on it yes. However the server grabs way more IPs from DHCP than the amount of VPN connections that are being used. Also the exchange server never has had any remote access setup on it and it’s a brand new virtual machine…

    configure less actual available VPN ports

    JeremyW
    JeremyW
    Moderator
    #270920

    Re: DHCP duplicate leases

    By default the VPN role will grab 10 addresses from DHCP. Once it’s used the 10 it will grab 10 more.

    You can modify this behavior by editing the registry.

    More info: http://technet.microsoft.com/en-us/library/cc958904.aspx

    Avatar
    bigalusn
    Participant
    #353872

    Re: DHCP duplicate leases

    1. DHCP shouldn’t be on your exchange server, so hopefully it’s not.
    2 scope what is your IP scope 10.10.10.xxx/24? (10.10 only example) if so that is 253 usable IP addresses.
    2. you can change your subnet to 10.10.10.xxx/22 and that will give over 1,000 usable IP addresses.

    JeremyW
    JeremyW
    Moderator
    #270930

    Re: DHCP duplicate leases

    bigalusn;287263 wrote:
    1. DHCP shouldn’t be on your exchange server, so hopefully it’s not.
    2 scope what is your IP scope 10.10.10.xxx/24? (10.10 only example) if so that is 253 usable IP addresses.
    2. you can change your subnet to 10.10.10.xxx/22 and that will give over 1,000 usable IP addresses.

    1. I haven’t heard any issues with an Exchange server running DHCP. It’s not recommended for Exchange to be on a DC but it is supported (like SBS and a single server setup)
    2. There’s 254 usable in a /24… or were you subtracting one for the gateway?
    2. (3.?) I would not recommend making this change without understanding the specific network. You wouldn’t want that many devices in the same broadcast domain. Not to mention the potential routing implications, possible use of public IPs, etc.

    Avatar
    Andrew Molan
    Member
    #390604

    Re: DHCP duplicate leases

    The company I am having difficulty in dealing with issues dividing ip . IT companies are less frequent dropouts

    Avatar
    Ossian
    Moderator
    #190063

    Re: DHCP duplicate leases

    Is this an answer to the original thread, or another question.

    Either way, I’m afraid it makes absolutely no sense at all!

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